How can I decode an object when original class is not available?

Question

I have an iOS 7 application that saves a custom object to app's iCloud Docs folder as a file. For this, I make use of NSCoding protocol.

@interface Person : NSObject <NSCoding>

    @property (copy, nonatomic) NSString *name
    @property (copy, nonatomic) NSString *lastName

@end

Object serialization works perfectly in iOS 7 version of the app:

1. initWithCoder and encodeWithCoder

2. [NSKeyedArchiver archivedDataWithRootObject:person]

3. person = NSKeyedUnarchiver unarchiveObjectWithData:(NSData *)theData]

But I need to move this app to iOS 8, and this class will be coded in swift and 'renamed' for this new iOS 8 version of the app.

class PersonOldVersion: NSObject, NSCoding {
    var name = ""
    var lastName = ""
}

When I try to unarchive the object I got the following error:

*** Terminating app due to uncaught exception 'NSInvalidUnarchiveOperationException', reason: '*** -[NSKeyedUnarchiver decodeObjectForKey:]: cannot decode object of class (Person)'

I already tried renaming swift class 'PersonOldVersion' to original class name ('Person') but still fails.

How can I decode an object which original class isn't available?

Answer 1

This might be another solution, and it's what I did (since I didn't use Swift at that time).

In my case, I archived an object of class "City" but then renamed the class to "CityLegacy" because I created a completely new "City" class.

I had to do this to unarchive the old "City" object as a "CityLegacy" object:

// Tell the NSKeyedUnarchiver that the class has been renamed
[NSKeyedUnarchiver setClass:[CityLegacy class] forClassName:@"City"];

// Unarchive the object as usual
NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
NSData *data = [defaults objectForKey:@"city"];
CityLegacy *city = [NSKeyedUnarchiver unarchiveObjectWithData:data];